Reliability Calculation And Structural Optimization Of Steel Truss With Implicit Function

Reliability is the main index for evaluating structural applicability and safety.The structural optimization should also focus on the reliability of the optimized structure in the pursuit of minimum construction cost or minimum weight.Therefore,it has been a key issue to how to obtain the reliability of structure accurately.Many scholars have done a lot of work on the calculation of the reliability of complex implicit function,but few methods can effectively coordinate the calculation accuracy,calculation amount and method adaptability and other aspects to calculate reliability.This paper takes the steel truss of Ai Zhai Bridge as an example to study the reliability and optimization of structure with complex implicit function.(1)The traditional genetic algorithm is improved by introducing adaptive random variables,adjusting the crossover rate and mutation rate in the process of evolution,and adding the elite retention strategy in this paper.Some examples prove that the Improved Genetic Algorithm(IGA)can adjust adaptively the value range of variables according to the value of fitness,jump out of local optimum effectively and accelerate the convergence speed.In addition,the adaptive random variable can greatly improve the gene of genetic algorithm for small probability failure structures.(2)In order to fit the structure function for genetic algorithm to call,there are three steps to do it.First of all,uniform design function in DPS(Data Process System)is adopted to generate a higher level of variables.And then ANSYS in batch mode is called by Python to calculate the structure responses.Finally,variables and responses are processed respectively by normalization method based on RBF neural network.Network test precision manifests that RBF neural network has good generalization ability with its high fitting accuracy.(3)Based on the geometric implication of reliability index,IGA is adopted to obtain the optimal solution of reliability index of steel trusses and its design point.Moreover,Monte Carlo Critical Sampling Method is introduced to verify the accuracy and validity of calculation method proposed in this paper at the design point.The result shows that IGA and Monte Carlo Method are employed respectively to calculate reliability of the steel truss,which proves that IGA has many advantages such as fast computation speed,simple computation and high precision when it calculates the reliability of structure with complex implicit function.(4)On the basis of the relationship between the well-fitted reliability and the design scalar,this paper uses the IGA to optimize the structure by taking the reliability index and the structural weight as constraints.The results show that if the structure decrease the beam cross section area and increase the area of section height and the web member,then the structural weight can be reduced on the premise of certain structural reliability and the optimized area is 13.9% less than before optimization.In addition,the structure reliability can be improved from 4.9310 to 5.8774 according to the weight of the design on the premise of constant structure weight.